Cationic latex compositions capable of producing elastomers with hydrophilic surfaces

ABSTRACT

Latex compositions suitable for applications requiring surface hydrophilicity are disclosed. The compositions comprise: (1) a liquid phase selected from the group consisting of water, water-miscible solvents and mixtures thereof; and (2) latex particles dispersed in the liquid phase. The particles comprise an elastomeric hydrophobic core and a hydrophilic &#34;shell&#34; which is integral with the core and which colloidally stabilizes the latex particles in the liquid phase. The shell comprises moieties L-Q attached to the core, wherein Q is a nonionic group end-capped with a cationic moiety, and L is a linking unit. When the liquid phase is removed, the particles are capable of forming an elastomeric film having a substantially permanent, cationic, hydrophilic surface. The cationic moiety helps the latex particles become attracted to anionic surfaces such as cellulosic materials.

TECHNICAL FIELD

The present application relates to latex compositions having surfacehydrophilicity.

Materials which have hydrophilic surfaces are easily wetted by water andother polar liquids. This should be contrasted with bulk hydrophilicitywhere the material "swells" in the presence of these polar liquids.Materials without bulk hydrophilicity having only surface hydrophilicitydo not swell, which can be highly desirable where "wet strength" isrequired. Materials which are bulk hydrophilic often have decreased wetstrength when swollen with water.

For many product applications the hydrophilic surface needs to have somedegree of permanency. Basically, this translates into the ability of thesurface to maintain wettability after repeated exposures to water orother polar liquids, as well as exposure to air. Permanency of thehydrophilic surface can be particularly difficult where the underlyingbulk material is hydrophobic, such as in the case of polyethylene orpolypropylene films. In these instances, the hydrophilic surface layerneeds to be compatible and adherent to the underlying bulk material;otherwise, the hydrophilic surface can be stripped away after relativelyfew exposures to water or other polar liquids. In addition, when theunderlying bulk material is soft or elastomeric, the surface layer canbe "swallowed up", resulting in a loss of surface hydrophilicity.

Surface hydrophilicity is preferably combined with other properties suchas flexibility, elasticity and strength. One category of materialsdesirably having such combined properties includes the binder systemsused in making non-woven fabrics and paper products. A variety of latexcompositions have previously been used as binders, including acrylic(methacrylic) latexes and styrene-butadiene latexes. These latexes aretypically formed by emulsion polymerization of the respective monomersand can optionally contain surfactants to stabilize the latex particles,as well as to impart a certain amount of hydrophilicity to the nonwovenproduct. These prior art latex binder systems tend to be nonwettable(hydrophobic) or to lose their wettability after repeated exposure towater. Additionally, the mechanical strength of these binders can varygreatly depending on changes in pH.

The cationic latex compositions herein are especially useful as additivebinder systems in making clothlike paper and other nonwoven products.

There are three important physical properties of clothlike paperproducts. These properties are softness; absorbency, particularly ofaqueous fluids; and strength, particularly strength when wet. Softnessis the tactile sensation perceived when the consumer holds the product,rubs it across the skin, or crumples it with the hand. This tactilesensation can be related to the stiffness of the paper product.Absorbency is a measure of the ability of the product to absorbquantities of liquid, particularly aqueous fluids or dispersions.Strength is the ability of the product to maintain physical integrity,and to resist tearing, bursting and shredding under use conditions,particularly when wet. Research and development efforts have beendirected to improvement of each of these properties without adverselyaffecting the others, as well as improvement of two or three of theseproperties simultaneously.

Water-soluble cationic resins are often used as wet-strength additivesin paper making. One such group of wet-strength additives are thepolyamide-epichlorohydrin resins sold under the trade name Kymene. See,for example, U.S. Pat. No. 3,700,623 to Keim issued Oct. 24, 1972; andU.S. Pat. No. 3,772,076 to Keim, issued Nov. 13, 1973. Another group ofwater-soluble cationic wet-strength resins are the polyacrylamides soldunder the trade name Parez. See, for example, U.S. Pat. No. 3,556,932 toCoscia et al, issued Jan. 19, 1971; and U.S. Pat. No. 3,556,933 toWilliams et al issued Jan. 19, 1971.

The cellulosic fibers used in papermaking are negatively charged. Sincethe water-soluble wet-strength resins are cationic (positively charged),they are deposited and retained well when directly added to the aqueouspulp slurry. Such "wet-end addition" is highly desirable in papermaking.Subsequently in the papermaking process, these resins cross-link andeventually become insoluble in water. When this occurs, the wet-strengthresin acts as a "glue" to hold the fibers of the paper together. Thisresults in the desired wet-strength property.

Paper products made with such resins generally have a stiff, paper-likefeel. To impart greater softness to the paper product, styrene-butadienelatexes can be used as the binder system. However, thesestyrene-butadiene latexes are either nonionic in character or else arepartially anionic due to inclusion of anionic comonomers or surfactants.The nonionic styrene-butadiene latexes cannot be used as "wet-endadditives" in a conventional papermaking process. Instead, thesenonionic latexes have to be impregnated or pattern-printed on thesubsequently laid paper furnish, such as by the process described inEuropean patent application No. 33,988 to Graves et al, published Aug.19, 1981.

An anionic styrene-butadiene latex can be used in a conventional wet-endadditive papermaking process by adding a cationic polyelectrolyte. See,for example, U.S. Pat. No. 4,121,966 to Amano et al, issued Oct. 24,1978; and U.S. Pat. No. 2,745,744 to Weidner et al, issued May 15, 1956.The cationic polyelectrolyte used is typically a water-soluble cationicwet-strength resin. Basically, the cationic polyelectrolyte, when added,destabilizes the dispersed anionic latex particles which then flocculateand deposit on the paper fibers. Accordingly, the cationicpolyelectrolyte and anionic styrene-butadiene latex cannot be combinedtogether until the point at which they are used as the binder system inpapermaking.

Styrene-butadiene latexes have also been modified to provide cationicgroups chemically bound on the surface of the latex particles. See, forexample, U.S. Pat. No. 4,189,345 to Foster et al, issued Feb. 19, 1980;and U.S. Pat. No. 3,926,890 to Huang et al, issued Dec. 16, 1975.Incorporation of the cationic groups on the surface of the latexparticles converts the latex into a wet-end additive like thewater-soluble cationic wet-strength resins. These cationic latexesappear to have adequate colloidal stability, especially when nonionic orpreferably cationic surfactants are added. However, the deposition andretention of the cationic latex particles on the paper fibers does notappear to be very great. Indeed, the cationic latex of the Foster et alpatent appears to require a co-additive to enhance the deposition of thelatex particles on the paper fibers.

Accordingly, a cationic latex which combines: (1) colloidal stability;and (2) enhanced deposition and retention of the latex particles on thepaper fibers, would be highly desirable.

Besides the papermaking art, there are circumstances where it would bedesirable to impart a cationic finish to surfaces such as fabrics inorder to provide an anti-static effect. The cationic latexes of thisinvention may be considered as substitutes for the quaternary ammoniumcompounds now typically used as anti-stats.

BACKGROUND ART A. Cationic Latexes Having Particles withStyrene-Butadiene Core and Cationic Groups Chemically Bound on Surface

U.S. Pat. No. 4,189,345 to Foster et al, issued Feb. 19, 1980, describesa fibrous product containing papermaking pulp, a structured-particlelatex having pH independent cationic groups bound at or near theparticle surface and a co-additive. The structured-particle latex has acopolymer core of styrene and butadiene, and an encapsulating layer ofstyrene, butadiene and vinylbenzyl chloride which is reacted with2-(dimethyl amino) ethanol to form quaternary ammonium groups. Theco-additive can be a hydrolyzed polyacrylamide having a degree ofpolymerization of 5500 and is used to enhance deposition of the cationiclatex on the pulp fibers. In making the fibrous product, thestructure-particle latex and an aqueous solution of the co-additive areadded to an aqueous slurry of the pulp, which is then dewatered anddried by heating.

U.S. Pat. No. 3,926,890 to Huang et al, issued Dec. 16, 1975, disclosesa process for preparing a "stable" cationic latex which is described ashaving "excellent adsorption" (only about 69% absorption of latex basedon Example 5) onto substrates such as pulp, paper and the like. TheHuang et al cationic latexes are prepared by emulsion polymerization ofa haloalkyl ester of acrylic or methylcrylic acid with anothermonosaturated compound and/or a conjugated diene compound (e.g.,butadiene) in the presence of a nonionic or preferably cationic surfaceactive agent, and then reacting a basic nitrogen-containing compoundwith this copolymer to form the respective ammonium salt.

B. Use of Cationic Polyelectrolytes to Enhance the Deposition of AnionicStyrene-Butadiene Latex Binder Systems on Paper Fibers

U.S. Pat. No. 4,121,966 to Amano et al, issued Oct. 24, 1978, disclosesa method for producing a fibrous sheet bonded with a latex flocculate.In this method, zinc white powders are added to a carboxy modifiedanionic latex. The pH of this mixture is adjusted to not less than 7,and then a water-soluble cationic polymer is added to obtain a latexflocculate. The latex flocculate is added to a fiber slurry which isformed into a sheet by a conventional papermaking process.Representative carboxy modified latexes include styrene-butadienecopolymers. Suitable water-soluble cationic polymers includepolyamide-polyamineepichlorohydrin resins, polyethylene imine resins,cationic modified melamine-formalin resins, and cationic modifiedurea-formalin resins.

U.S. Pat. No. 2,745,744 to Weidner et al, issued May 15, 1956, disclosesa method for incorporating polymeric or rubberlike materials intocellulosic fibers used to make paper. In this method, a colloidaldispersion of a hydrophobic polymer, such as a butadiene-styrene latex,is mixed with a paper pulp suspended in water. A poly-N-basic organiccompound is then added to this mixture to cause particles of thecolloidal dispersed material to adhere to the cellulosic fibers in thewater suspension. The treated fiber is then formed into paper byconventional techniques.

SUMMARY OF THE INVENTION

The present invention encompasses latex compositions which comprise:

(1) a liquid phase selected from the group consisting of water,water-miscible solvents and mixtures thereof;

(2) latex particles dispersed in said liquid phase, said particlescomprising an elastomeric hydrophobic core and an outer hydrophilicshell integral with said core, said shell comprising moieties L-Q,attached to the core, wherein Q is a hydrophilic group and L is ahydrophobic unit.

Preferred compositions herein comprise:

(a) an aqueous phase;

(b) from about 5 to about 50% by weight of latex particles dispersed insaid aqueous phase, said particles comprising an elastomeric hydrophobiccore and an outer hydrophilic shell attached to said core, said corecomprising a polymer selected from the group consisting of butadiene,isoprene, styrene, and mixtures thereof, and said shell comprisingmoieties L-Q, wherein L comprises a hydrophobic hydrocarbyl groupcontaining one or more unsaturated bonds and Q is of the formula##STR1## wherein R¹ and R² are each C₁ to C₄ alkyl or hydroxyalkyl, ortogether form a cyclic or heterocyclic ring, and R³ is H or C₁ -C₄ alkylor hydroxyalkyl, and wherein n is an integer of from 5 to about 50.

The invention also encompasses a process for preparing a latexcomposition which comprises the steps of:

(A) providing a mixture containing:

(a) water;

(b) a dispersion of from about 5 to about 50% of a substantiallywater-insoluble polymerizable component which comprises an elastomermonomer having double bonds;

(c) an effective amount of a water-soluble free-radical polymerizationinitiator;

(d) an effective amount of a water-soluble chain transfer agent; and

(e) an effective amount of an amphiphilic diblock emulsifier LQ whichcomprises an unsaturated hydrophobic moiety L having one or morecarbon-carbon double bonds and a hydrophilic block Q integral with saidhydrophobic block; said hydrophilic block Q being a nonionic groupend-capped with a cationic moiety; and

(B) heating the mixture to a temperature sufficient to cause emulsionpolymerization of the polymerizable component, so as to provide a latexcomposition comprising latex particles capable of forming an elastomericfilm having a substantially permanent hydrophilic surface when the wateris removed.

A preferred process herein is wherein elastomer monomer (b) is a memberselected from the group consisting of butadiene, isoprene, styrene, andmixtures thereof. Preferably, the diblock emulsifier (e) comprises aquaternary ammonium capped polyethyleneoxide derivative of a C₁₀ -C₂₀unsaturated hydrocarbyl moiety.

The invention also encompasses a process for improving the tactileimpression of paper or fabric, comprising contacting said paper orfabric with the foregoing latex compositions and drying said paper orfabric. In an alternate mode, the process comprises contacting saidpaper or fabric with a mixture of a cationic hydrophilic latex of thisinvention and an anionic hydrophilic latex; more preferably, a mixedcationic/nonionic latex is used. Paper or fabric articles prepared inthis manner also form part of this invention.

The invention also encompasses compounds of the formula LQ, wherein L isa hydrocarbyl moiety having at least one carbon-carbon double bond and Qis a nonionic group end-capped with a cationic moiety. Preferredcompounds are those wherein Q is ethylene oxide end-capped with aquaternary ammonium moiety, as noted above. Conveniently, L can be amember selected from the group consisting of oleyl (preferred),linoleyl, linolenyl, eleostearyl, and parinaryl. An especially preferredcompound herein is oleyl[EO]₁₉ OCH₂ CH₂ N⁺ (CH₃)₃ Br⁻.

DISCLOSURE OF THE INVENTION

The present invention relates to cationic latex compositions. Thesecompositions comprise:

(a) a liquid phase which is selected from the group consisting of water,water-miscible solvents, and mixtures thereof;

(b) an effective amount of latex particles dispersed in the aqueousphase;

(c) said particles comprising an elastomeric hydrophobic core and anouter cationic hydrophilic surface (or "shell") integral with the core;

(d) said hydrophilic surface comprising moieties L-Q or, optionally, amixture of moieties L-Q and L-X attached to the core, wherein Q is anonionic group end-capped with a cationic moiety, X is a nonionic group,and L is a linking group which chemically bonds to the elastomeric core.

The hydrophilic shell of the particles ultimately translates into thehydrophilic surface of the films formed therefrom. The outer surface ofthe latex particles also is sufficiently hydrophilic to colloidallystabilize the particles in the aqueous phase so they do not flocculate.Moreover, this outer shell has sufficient cationic charge density tocause deposition and retention of the latex particles on negativelycharged surfaces such as cellulosic fibers. Accordingly, the cationiclatex compositions of the present invention can be used as wet-endadditive binders in making paper or other nonwoven products.

A. Definitions

As used herein, the term "hydrophilic" refers to materials which aresubstantially wetted by water.

As used herein, the term "hydrophobic" refers to materials which aresubstantially non-wetted by water.

As used herein, the term "elastomeric" refers to materials havingrubber-like properties in terms of extensibility and elastic recovery.See Condensed Chemical Dictionary (9th edition 1977), page 335, whichdefines the term "elastomer".

As used herein, the term "comprising" means various components can beconjointly employed in the latex compositions of the present invention.Accordingly, the term "comprising" encompasses the more restrictiveterms "consisting essentially of" and "consisting of".

All percentages, ratios and proportions herein are by weight, unlessotherwise specified.

B. Cationic Latex Compositions

The cationic latex compositions of the present invention basicallycomprise: (1) an aqueous phase; and (2) latex particles dispersed in theaqueous phase to form a colloidally stable suspension thereof. Besideswater, this aqueous phase can include minor amounts of water-misciblesolvents. Suitable water-miscible solvents include the C₁ -C₃ alcohols,such as methyl alcohol, ethyl alcohol and isopropyl alcohol, ketonessuch as acetone, and other water-miscible solvents such as ethylacetate. However, the aqueous phase is typically substantially free,i.e., contains less than about 1% by weight, of these water-misciblesolvents.

The key component of the latex composition is the latex particlesdispersed in the aqueous phase. These latex particles are generallyspherical in shape and are monodisperse in size, i.e. the particlessizes fall within a narrow range. These particles can sometimes be aslarge as several microns or as small as 10 nm. However, because thelatex particles are typically formed by emulsion polymerization, theseparticles tend to be submicron in size. Typically, the particle size ofthese latex particles is in the range of from about 50 to about 100 nm.

These latex particles are dispersed in the aqueous phase in an effectiveamount. What is "an effective amount" of latex particles depends uponthe particular use of the latex composition, the manner in which it isformed, and like factors. Latex compositions having high solids contentof latex particles are preferred. Latex compositions of the presentinvention may comprise up to about 60% by weight latex particles on asolids basis. Typically, the latex particles comprise from about 10% toabout 20% by weight of the latex composition on a solids basis.

The latex particles are comprised of both: (1) an elastomerichydrophobic core; and (2) an outer cationic hydrophilic surface, orshell, which is integral with the elastomeric core. The shell can beintegral with the core through either: (1) physical attachment; or (2)chemical attachment. For reasons of permanence, the shell is preferablychemically attached to the core. Chemical attachment results throughcovalent bonding of the shell to the core.

The elastomeric hydrobic core is the predominant component of the latexparticles by weight. This elastomeric core is based on a polymer formedfrom an elastomer, typically in combination of other comonomers, toimpart properties such as stiffness, strength, resistance to flowabilityat elevated temperatures, etc. The polymers which form the elastomericcore usually have glass transition (T_(g)) values of about 35° C. orless. Preferred polymers for elastomeric cores preferably have T_(g)values of about -10° C. or less.

The cationic hydrophilic surface is the primary functional component ofthe latex particles. The surface of the latex particles has twoessential functions. The first is to provide sufficient hydrophilicityto colloidally stablize the latex particles in the aqueous phase so asto prevent flocculation. The other function of this shell is to providesufficient cationic charge density to cause deposition and retention ofthe latex particles on negatively charged surfaces, especiallycellulose. For example in a papermaking process, latex particles whichare not retained by the fibers can accumulate in the process water andcontaminate the papermaking machinery; accordingly, it is desirable tomaximize the amount of latex which is deposited and retained on thefibers. For cationic latex compositions of the present inventory thiscationic charge density is sufficiently great to cause deposition andretention of as much as about 80-90% by weight of the latex particles onthese fibers.

Moreover, the hydrophilic properties of the latexes herein can be usedto impart "water-wettability" to otherwise hydrophobic surfaces, asdescribed more fully, hereinafter.

The surface, or shell, of the latex particles comprises moieties L-Q or,optionally, a mixture of moieties L-Q and L-X attached to theelastomeric core, wherein Q is an alkoxylated cationic group, X is anonionic group and L is the linking unit. These materials havesurfactant and emulsifier properties, and are referred to as "diblocks".

The cationic group Q can be any compatible positively charged moietywhich can cause deposition of the latex particles onto negativelycharged cellulosic fibers. Suitable cationic groups Q includesubstituted ammonium groups having the formula: ##STR2## where R¹ and R₂are each C₁ C₄ alkyl or hydroxyalkyl, or together form a cyclic orheterocyclic ring of from 4 to 6 carbon atoms (e.g., piperidine,morpholine); and R³ is H (ammonium) or C₁ -C₄ alkyl or hydroxyalkyl(quaternary); and EO is ethyleneoxy with n being an integer of fromabout 5 to 50, preferably 10 to 20. Particularly preferred substitutedammonium groups are those where R¹, R² and R³ are each methyl. Suitablecationic groups Q also include sulfonium groups having the formula:##STR3## where R¹ and R² are defined as before. Preferred sulfoniumgroups are those where R¹ and R² are each methyl.

Of course, the cationic substituents will be associated with an anionicsubstituent (A) to provide electrical neutrality. The nature of A is notcritical to the practice of this invention. Anions such as halide,hydroxide and the like are typical; bromide is preferred.

The nonionic group X in nonionic diblocks can be any compatibleneutrally charged moiety which does not substantially interfere withcolloidal stability, or deposition and retention characteristics of thelatex particles. Suitable nonionic groups X include hydroxyl, andpreferably, polyethyleneoxide (EO units 5-50, preferably 10-20).

Linking unit "L" is any group which provides secure attachment of Q andX groups to the latex particles. As will be disclosed in more detailhereinafter, L is preferably an unsaturated hydrocarbyl species,especially oleyl.

The following Examples illustrate the preparation of the cationicdiblock materials herein, as well as their use in a papermaking process.In general terms, addition of the cationic latex to a cellulose fiberslurry should be done with good mixing. If not properly mixed, itappears that the latex can cause clumping of the fibers.

C. Methods for Preparing Cationic Latex Compositions

1. Emulsion Polymerization

One method for preparing the cationic latex compositions of the presentinvention is by emulsion polymerization. In emulsion polymerization, acationic (or mixed cationic and nonionic) diblock emulsifier of theforegoing LQ or mixed LQ and LX types is dispersed in water. Awater-soluble free-radical initiator is then added and optionally awater-soluble chain transfer agent is also added to control themolecular weight of the latex particles formed during emulsionpolymerization. A polymerizable component containing elastomer monomer,plus any comonomer, is added and the mixture is then heated to atemperature suitable for emulsion polymerization.

During emulsion polymerization, the diblock emulsifier stabilizes themonomer droplets of the polymerizable component dispersed in the aqueousphase and forms micelles which become swollen with monomer(s) from thedispersed droplets. While not intending to be limited by theory, itseems that the free-radical initiator diffuses into the monomer-swollenmicelles and initiates polymerization of the monomer(s) to form thelatex particles. The diblock emulsifier on the surface of the micellessolvates additional monomer and stabilizes the forming latex particles.Eventually, the diblock emulsifier becomes grafted or embedded onto theelastomeric core of the particle to form the cationic, or mixedcationic/nonionic hydrophilic shell.

A variety of elastomer monomers can comprise the polymerizablecomponent. The only requirements are that the monomer be water-insolubleand have at least one double bond. Examples of suitable elastomermonomers include butadiene, isoprene and mixtures thereof. Thepolymerizable component can also include other comonomers or mixtures ofcomonomers which impart stiffness and strength, cross-linking capabilityto control flowability at elevated temperatures or other desirableproperties to the latex particles. Examples of such comonomers includestyrene, alphamethyl styrene, vinyl toluenes, divinyl benzene, vinylacetate, acrylic acid, methacrylic acid, acrylonitrile,methacrylonitrile, acrylamide, methacrylamide, methyl acrylate, ethylacrylate and like acrylates, methyl methacrylate, ethyl methacrylate andlike methacrylates, maleic anhydride, fumaric acid, itaconic acid,crotonic acid, ethylene, propylene, and mixtures thereof.

Usually, the polymerizable component comprises from about 5 to about 50%by weight of the aqueous phase. Preferably, the polymerizable componentcomprises from about 10 to about 25% by weight of the aqueous phase. Theelastomer monomer(s) usually comprises from about 40 to 80% by weight ofthe polymerizable component, while the comonomer(s) comprises from 0 toabout 60% by weight of the component. Preferably, the elastomermonomer(s) comprises from about 60 to about 100% by weight of thecomponent, while the comonomer(s) comprise from about 0 to about 40% byweight of the component. Particularly preferred polymerizable componentscomprise from about 50 to about 75% by weight butadiene (or isoprene)and from about 25 to about 50% by weight styrene or a mixture of styrenewith up to 2% by weight divinylbenzene. Such batadiene-styrene orisoprene-styrene mixtures can optionally comprise up to about 10% byweight acrylic acid or methacrylic acid.

A particularly important component in this emulsion polymerizationprocess of the present invention is the cationic (or mixed cationic andnonionic) diblock emulsifier. The diblock emulsifier is used in aneffective amount in the emulsion polymerization process. What is "aneffective amount" depends upon the particular emulsifier being used, thetype of cationic latex composition desired, and like factors. Usually,the diblock emulsifier comprises from about 2 to about 20% by weight ofthe polymerizable component. Preferably, the diblock comprises fromabout 4 to about 10% by weight of the polymerizable component.

A particularly important factor in determining what diblock emulsifierto use is the ability of the emulsifier to become grafted to the core ofthe formed latex particles. As long as this key factor is satisfied, theselection of the diblock emulsifier is essentially a matter of whatproperties are desired in the cationic latex composition. This diblockemulsifier can consist entirely of the cationic diblock, or is typicallya mixture of cationic diblock and nonionic diblock. Usually, the weightratio of cationic diblock to nonionic diblock in the mixture ranges fromabout 1:5 to about 5:1; preferably 1:1 to 1:5, most preferably thisweight ratio is from about 1:2 to about 1:3.

D. Preparation of Cationic End-capped Diblock

The general reaction sequence for the synthesis of cationic diblockmaterials LQ used herein involves preparing the tosylate derivative (2)of the LX ethoxylate (1), followed by amination to form amine (3) andreaction with an alkyl halide to form the quaternized end-capping group(4), according to the following reaction sequence: ##STR4##

A typical synthesis is as follows:

Preparation of Oleyl(EO₁₉)OCH₂ CH₂ N(CH₃)₃ ⁺ Br⁻ A recrystallized sampleof p-toluenesulfonyl chloride (550 g; 2.9 moles) was added in twobatches (20 min apart) to a solution of 3.0 kg (2.6 mole) of oleylethoxylate (EO₂₀) and 871 g (8.61 mole) of triethylamine in 10 L ofacetonitrile under an argon atmosphere at room temperature (25°-30° C.).The mixture was stirred for three days at room temperature and then wasfiltered and concentrated. Three liters of water were added and themixture was extracted three times with methylene chloride. The organiclayers were combined, dried, filtered and concentrated yielding 3336 gof a viscous oil, oleyl (EO₁₉)CH₂ CH₂ OTs: 1H NMR 7.8 (d, Ar), 7.4 (d,Ar), 5.3 (t, ═CH), 3.4-3.9 (m, OCH₂), 2.4 (s, ArCH₃), 2.0 (m, ═CCH₂),0.9-1.6 (m, CH.sub. 3 CH₂). The oil was taken up in 1 gal ofacetonitrile and 1654 mL of condensed dimethylamine was added. Themixture was stirred overnight at room temperature and then the excessamine and acetonitrile were removed under a vacuum. While the mixturewas heated with a hot water bath, 3 L of 5% sodium hydroxide were addedand the mixture was extracted with methylene chloride. The organiclayers were combined, dried, filtered and evaporated yielding 2305 g ofoleyl (EO₁₉)CH₂ CH₂ N(CH₃)₂ : 1H NMR 5.3 (t, ═CH), 3.4-3.9 (m, OCH₂, 2.5(t, NCH₂), 2.3 (s, NCH₃, 2.0 (m, ═CCH), 0.9-1.6 (m, CH₃ CH₂). The oleyl(EO₁₉)OCH₂ CH₂ N(CH₃)₂ was dissolved in 1 gal of acetonitrile and thenmethyl bromide was bubbled into the solution which was initially at roomtemperature. The temperature rose to 48° C. The addition was continuedfor 2.5 h until the excess methyl bromide began refluxing. The mixturewas stirred for 3 h at room temperature and then concentrated. A ¹³ CNMR analysis indicated that up to 5% of the amine remained ureacted. Thecrude product was redissolved in 4 L of acetonitrile and methyl bromidewas bubbled into the solution for 45 min. 50 mL of 10% sodium carbonatewas added and the mixture was stirred at 40° C. overnight. The mixturewas then filtered and concentrated yielding 2439 g of oleyl (EO₁₉)OCH₂CH₂ N(CH₃)₃ ⁺ Br⁻ : 1H NMR 5.3 (t, ═CH), 3.4-3.0 (m, OCH₂), 3.45 (s, N⁺CH₃), 2.0 (═CCH₂). 0.9-1.6 (m, CH₃ CH₂). By negative cationic titration,Total Cationic=87.5% [N⁺ (CH₃)₃ plus N⁺ H(CH₃)₂ ] and Quaternary=82.2%[N⁺ (CH₃)₃ only].

E. Optional Nonionic Diblock

It will be appreciated that the nonionic materials (LX) which may beused as the optional, but preferable nonionic diblocks herein, and whichare used in the synthesis of the cationic end-capped diblock materialscomprise typical ethoxylated alcohol derivatives of alkenyl and/orpolyunsaturated hydrocarbyl groups, generally in the chain length rangeof from about 10 to about 22 carbon atoms and include, for example,hydrocarbyl groups derivable from such materials as oleic acid, linoleicacid, linolenic acid, eleostearic acid, parinaric acid, and the like.Other unsaturated groups include oligomeric and polymeric materialshaving residual double bonds, including polybutadiene mixtures,polyisoprene mixtures, and the like. The oleyl group is a preferredunsaturated hydrocarbyl group in the nonionic di-block materials herein.

The polyoxyalkylene substituents on LX are of the formula (OCH₂ CH₂)_(n)--OH, where n is an interger from about 5 to about 50, preferably fromabout 10 to about 20. It will be readily appreciated by those skilled inthe emulsifier arts that these nonionic materials fall within the classof well-known ethoxylated alcohol nonionic surfactants, with the provisothat the hydrocarbyl substituent have one or more points of unsaturationwhich allow the material to become involved in the polymerizationprocess, thereby chemically bonding the material to the latex particles.A commercially available material of this type is available under thetrade name "VOLPO-20", which comprises an oleyl group and an average of20 ethoxylate units.

The following examples illustrate the practice of this invention in moredetail, using the above-disclosed quaternary and nonionic diblocks.

EXAMPLE I

A wet-end-depositable cationic latex based on styrene-butadiene rubberwas prepared in the following manner. A mixture of a surfactant solutionprepared by dissolving 6.44 g of oleyl ethoxylate having approximately20 ethoxylate units in 500 mL of distilled water, another surfactantsolution prepared by dissolving 2.15 g of derivatized oleyl ethoxylatehaving approximately 20 ethoxylate units with a quaternary ammoniumfunctional group attached to the terminal end of the ethoxylate chain in150 mL of distilled water, an initiator solution prepared by dissolving0.72 g of 2,2'-azobis(2-amidinopropane) dihydrochloride in 50 mL ofdistilled water, and additional 301 mL of distilled water was placed ina 2 L stainless steel high-pressure reactor equipped with a mechanicalstirrer. The distilled water used in this reaction was purged with argonbefore being used, and the reactor was flushed with nitrogen gas beforethe solution mixture was placed inside. The reactor containing thesolution mixture was further purged with argon gas for one hour, then0.72 g of divinylbenzene and 57.2 g of styrene were injected into thereactor. The transfer of 85.8 g of 1,3-butadiene into the reactor wascarried out by condensing it in a 100 mL graduated cylinder first andthen injecting the condensate. The reactor was sealed and the reactionmixture was heated to 60° C. and maintained at the constant temperaturethroughout the reaction with slow agitation with the mechanical stirrerfor 18 hours to complete the emulsion polymerization.

A solid content of the latex product was estimated by the followingmethod. Approximately 2 mL of the latex was dried in an oven at 110° C.for at least one hour. From the weight of this sample before and afterdrying, the solid content of the latex was calculated to be 13.1%. Theparticle size (diameter) of the latex measured by quasi-elastic lightscattering was 0.154±0.036 μm. The surface hydrophilicity of the solidproduct made from the latex was also measured. A solid film sample ofthe latex was obtained by placing 1.0 mL of the reaction product onto a2.5 cm×7.5 cm glass plate and allowing to dry at room temperature forseveral days. The surface hydrophilicity of the film was determined byplacing 4 μL of distilled water over the film which was kept horizontaland observing the contact angle between the film surface and watersessile drop using a horizontal microscope equipped with a goniometer.The contact angle of water averaged over six measurements was 8.2±1.0°.

The wet-end depositability of the cationic latex onto the surface ofwood pulp was verified in the following manner. A mixture of thecationic latex and a refined Krafft pulp suspension in water with 0.1%consistency by weight was prepared such that the dry-weight ratiobetween the pulp and latex became about 5:1. Using sulfuric acid, the pHof the mixture was adjusted to 4.5. The turbidity of the mixturedecreased quickly and became clear within 30 minutes under gentleagitation at room temperature. Observation of pulp under a microscopeconfirmed that latex particles were deposited onto the surface of pulpfibers.

The efficacy of the latex as a wet-strength improving additive for paperand cellulosic nonwoven products was tested by forming a handsheet. A 12in×12 in handsheet weighing 2.5 g was prepared from a mixture ofuntreated refined Krafft pulp and similar Krafft pulp treated with thecationic latex. The weight ratio between the untreated pulp and pulptreated with the latex was 4:1, and the total add-on level of the latexin the handsheet was 4%. The handsheet was drum dried first and thenpressed at 50 psi for a minute at 110° C. The wet-strength of thehandsheet was determined by measuring the tensile strength required totear a one-inch-wide strip of the handsheet after the sample was soakedwith water. The wet-strength measured for the latex containing handsheetwas 199±22 g/in.

EXAMPLE II

A wet-end-depositable cationic latex based on styrene-butadiene rubberwas prepared in the manner similar to Example I. A reaction mixturehaving identical compositions described in Example I except without theaddition of divinylbenzene was placed in a sealed 2 L stainless steelhigh-pressure reactor equipped with a mechanical stirrer. The mixturewas then heated to 60° C. and maintained at the temperature 47 hourswith slow agitation to complete the emulsion polymerization. A latexcontaining 12.3% solids by weight, determined by the method described inExample I, was obtained.

The surface-hydrophilicity of the solid product made from the latex wasmeasured by the method described in Example I. The average contact angleof a sessile water drop placed on the surface of a film prepared fromthe latex was 7.2±1.0°. The wet-end depositability of the latex onto thesurface of wood pulp was verified, and the wet tensile strength of ahandsheet containing 4% latex was measured by the methods described inExample I. The average wet strength was 341±14 g/in.

EXAMPLE III

A wet-end-depositable cationic latex based on styrene-butadiene-acrylicacid copolymer rubber was prepared in the following manner. A mixture ofa surfactant solution prepared by dissolving 0.32 g of oleyl ethoxylatehaving approximately 20 ethoxylate units in 15 mL of distilled water,another surfactant solution prepared by dissolving 0.105 g ofderivatized oleyl ethoxylate having approximately 20 ethoxylate unitswith a quaternary (trimethyl) ammonium fuctional group attached to theterminal end of ethoxylate chain in 15 mL of distilled water, aninitiator solution prepared by dissolving 0.142 g of2,2'-azobis(2-amidinopropane) dihyrochloride in 15 mL of distilledwater, and additional 11.4 mL of distilled water was placed in a 250 mLthick-walled glass reaction bottle with a magnetic stirring rod. Thedistilled water used in this reaction was purged with argon for 15minutes before being used. The reaction bottle containing the solutionmixture of surfactants and initiator was flushed with nitrogen andsealed with a rubber gasket which was covered with a metal bottle capwith two holes. The transfer of 0.53 g of acrylic acid, 0.073 g ofdivinylbenzene, and 1.75 g of styrene into the reaction bottle was madeby injecting the monomers through the rubber gasket with a syringe. Thetransfer of 5.25 g of 1,3-butadiene was made by condensing it first in a15 mL graduated cylinder submerged in dry ice and injecting thecondensate into the reaction bottle with a syringe. The reaction bottlewas then placed in an oil bath set at 60° C. throughout the reactionperiod with slow agitation of the reaction mixture with a magneticstirrer for 16 hours to complete the emulsion polymerization. A latexhaving a solid content of 10.4% was obtained. The wet-end depositabilityof the latex was verified by the method described in Example I.

EXAMPLE IV

A wet-end-depositable cationic latex based on styrene-butadiene rubbersynthesized with anionic free radical initiator was prepared in themanner similar to Example III. A solution mixture prepared by dissolving0.28 g of oleyl ethoxylate surfactant having approximately 20 ethoxylateunits, 0.07 g of derivatized oleyl ethoxylate surfactant havingapproximately 20 ethoxylate units with a quaternary ammonium functionalgroup attached to the terminal end of ethoxylate chain, and 0.035 g ofpotassium persulfate free-radical initiator in 56.4 mL of distilledwater was placed in a 250 mL thick-walled glass reaction bottle with amagnetic stirring rod. The distilled water was purged with argon for 15minutes before being used. The reaction bottle containing the solutionmixture of surfactants and initiator was flushed with nitrogen andsealed with a rubber gasket covered with a metal cap and two holes. Thetransfer of 1.75 g of styrene and 5.25 g of 1,3-butadiene into thereaction bottle was carried out with a syringe as described in ExampleIII. The reaction bottle was placed in an oil bath set at 60° C.throughout the reaction period with slow agitation of the reactionmixture with a magnetic stirrer for 16 hours to complete the emulsionpolymerization.

The solid content of the latex determined by the method described inExample I was 7.6%. The surface hydrophilicity of the solid product madefrom the latex was measured by the method described in Example I. Theaverage contact angle of a sessile water drop placed on the surface of afilm prepared from the latex was 5.8±0.8°.

EXAMPLE V

A wet-end-depositable cationic latex based on styrene-butadiene rubbersynthesized in the presence of cationic surfactant was prepared in themanner similar to Example III. A solution mixture prepared by dissolving0.105 g of derivatized oleyl ethoxylate surfactant having approximately20 ehtoxylate units with a quaternary ammonium functional group attachedto the terminal end of ethoxylate chain and 0.035 g of2,2'-azobis(2-amidinopropane) dihydrochloride free-radical initiator in49 mL of distilled water was placed in a 250 mL thick-walled glassreaction bottle with a magnetic stirring rod. The distilled water waspurged with argon before being used. The reaction bottle containing thesolution mixture of surfactant and initiator was sealed with a rubbergasket covered with a metal cap with two holes. The transfer of 2.8 g ofstyrene, 4.2 of 1,3-butadiene, and 0.035 g of divinylbenzene was carriedout with a syringe as described in Example III. The reaction bottle wasplaced in an oil bath set at 60° C. throughout the reaction period withslow agitation of the reaction mixture with a magnetic stirrer for 17hours to complete the emulsion polymerization.

The solid content of the latex determined by the method described inExample I was 12.5%. The wet-end depositability of the latex onto thesurface of wood pulp was verified, and the wet tensile strength of ahandsheet containing 4% latex was measured by the methods described inExample I. The average wet strength was 61±2 g/in.

EXAMPLE VI

The applicability of a cationic latex as a wet-end additive for acontinuous papermaking process was demonstrated in the following manner.Approximately 500 dry pounds of refined northern softwood Kraft pulp wasdispersed in water at the consistency of about 2.5% and kept in astirred holding tank. The pH of pulp mixture was adjusted to 4.5 withsulfuric acid. About 100 gal. of cationic latex prepared according to arecipe similar to that described in Example I was added to the pulp toachieve the wet-end deposition of the binder. The extent of thedeposition process was determined by centrifuging samples obtained fromthe pulp mixture and checking the turbidity of the supernatant. Theturbidity due to the undeposited latex particles disappeared within 30minutes.

The latex-treated pulp was then fed to a pilot scale paper machine(equipped with normal papermaking process components, such as headbox,forming wire, and continuous dryer) at a rate of about 20 gal/min. Thepaper machine was operated at the production speed of 800 ft/min,producing paper products having a basis weight around 15 lb/3000 ft².Samples of paper products were collected after the paper machineoperation approached sufficiently close to the steady state.

The latex content of the final paper products was measured by x-rayfluorescence analysis. The analysis was done by brominating theunsaturated double bonds of a styrene-butadiene rubber component of thelatex and then measuring the x-ray fluorescence intensity. The estimatedlatex add-on level for the sample measured by this method was 11.6±1.2%.The wet strength of the latex-containing paper product produced by acontinuous pilot paper machine was determined by measuring the tensilestrength required to tear a one-inch-wide strip of paper product afterthe sample was soaked in water. The wet strength measured for thelatex-containing paper was 153 g/in. In comparison, the wet strength ofa paper product, produced by a similar process using the same pilotpaper machine but without the addition of latex binder, did not exceed25 g/in.

What is claimed is:
 1. A latex composition which comprises:(a) anaqueous phase; (b) from about 5 to about 50% by weight of latexparticles dispersed in said aqueous phase, said particles comprising anelastomeric hydrophobic core and an outer hydrophilic shell attached tosaid core, said core comprising a polymer selected from the groupconsisting of butadiene, isoprene styrene, and mixtures thereof, andsaid shell comprising moieties L-Q, wherein L comprises a hydrophobichydrocarbyl group containing one or more unsaturated bonds and Q is ofthe formula ##STR5## wherein R¹ and R² are each C₁ to C₄ alkyl orhydroxyalkyl, or together form a cyclic or heterocyclic ring, and R³ orC₁ -C₄ alkyl or hydroxyalkyl, and wherein n is an integer of from 5 toabout
 50. 2. A latex according to claim 1 which comprises a mixed shellof LQ and LX substituents, wherein L and Q are as defined above and X isa nonionic substituent.